It is possible that the UFP did not actually use Earth measurements, but that their usage on screen is an example of "implicit translation" (such as the characters in the film K-19: The Widowmaker speaking English when the viewer understands that they are "speaking" Russian.) This is implied by scenes such as the one where Kirk remarks to Abraham Lincoln that the Enterprise could convert to minutes. (TOS: "The Savage Curtain")

A cc (cubic centimeter, official cm3) was a measure of volume equal to one cubic centimeter (cm3), which was also equal to one milliliter (ml). The cc was a common term for milliliters used in measuring the dosage of liquid medicines by volume.